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The Role of Various Modes of Adsorbed CO in Synthesis Gas Conversion on Lanthanide Ions Promoted by Supported Pd Catalysts
OUni, L et d.(Editon), New Frontiers in Caraljsk
Proceedings of the 10th International Congress on Catalysis, 19-24 July, 1992, Budapest, Hungary 0 1993 Elsevier Science Publishers B.V.All rights reserved
THE ROLE OF VARIOUS MODES OF ADSORBED CO IN SYNTHESIS GAS CONVERSION ON LANTFIANIDE IONS PROMOTED BY SUPPORTED Pd CATALYSTS Yu. N. Nogina, N. V. Chesnokovband V. I. Kovalchukb
aInstituteof Catalysis, Russian Academy of Sciences, Siberian Division, 5 Akademika Lavrentieva Str., 630090 Novosibirsk, Russia bInstitute of Chemistry of Natural Organic Materials, 42 K. Marx Str., 660049 Krasnoyarsk, Russia
1. INTRODUCTION
Some dispersed supported metals (for example Pd or Rh) show catalytic activity in vapor phase olefin hydroformylation. The reaction can be used for the study of migratory CO insertion as an elementary step in the alcohols formation and chain propagation in synthesis gas conversion. It is known that the modification of supported rhodium by Fe(II1) ions results in the enhancement of oxygenates formation in propylene hydroformylation. This fact has been accounted by the promotion of migratory CO insertion due to its bi-site activation on surface bimetallic Rh-Fe3+ ensembles [ 11. To understand the role of CO adsorption mode in synthesis gas conversion on modified supported Pd catalysts we have studied propylene and hexene- 1 hydroformylation on supported Pd+Ln and Pd catalysts. 2. EXPERIMENTAL
Silica (surface area, 250 m'g-') and lanthana (60 m'8-I) were used as supports. Tris (isopropylcyclopentadienyl)complexes of Ln and allylpalladiumcyclopentadieny 1 were used as initial compounds. (Pd+Ln)/support catalysts were prepared in an inert atmosphere as described elsewhere [2]. IR spectra were recorded on a Bruker IFS-113 V Fourier spectrometer within 1300-4000 cm-' with a resolution of 4 cm-' as described elsewhere [3]. Temperature programmed desorption (TPD) of hydrogen was carried out following treatment of catalysts by hydrogen at 5OoCand cooling the sample in Hz flow to room temperature. Moreover, the TPD of HZwas carried out following hydrogen processing at 3OO0C and cooling the catalyst in Ar flow to 5OoCand HZadsorption. TPD of CO and propylene was carried out following catalysts reduction by hydrogen at 5OO0C and cooling the sample in helium to room temperature and appropriate gas adsorption.
2032 CO hydrogenation was performed on catalysts reduced at 3OO0C in a copper flow reactor at 25OoC, 10 atm, CO:Hz'l:2, space feed velocity 20 000 h-' with a conversion of <1% as described previously [2]. The activity and selectivity were determined in 30 min upon reaction start. Propylene and hexene- 1 hydrofoimylation was performed on catalysts without any preliminary treatment in a glass flow reactor at 5OoC, 1 atm, C0:Hz:olefin = 1:l:l with a conversion of <5%. Steady state activity and selectivity were determined. 3. RESULTS AND DISCUSSION
FTIR studies of CO adsorption were performed on Ln-containing and unmodified sup orted Pd catalysts. For CO two absorption bands within 2103-2060 and 1975-1900 cm- were reasonably assigned to linear and bridging carbonyl on Pd atoms, respectively. A low-frequency band within 1628-1600 cm-' on modified catalysts can be attributed to CO adsorbed on mixed Pd-Ln"' sites. The reactivity of surface carbonyl species on (1.O%Pd+5.0%Pr)/SiOz catalyst in relation to hydrogen has been investigated.The low-frequency CO adsorption mode does not seem to have the highest reactivity. The results of H2 TPD study for a number of (Pd+Ln) h i 0 2 catalysts are presented on Fig. 1. There are two adsorbed modes of H2 desorbing within 85-12OoC and 365-420°C, with negligible amount of hydrogen being desorbed at low temperature. A considerable part of palladium surface in modified catalysts is, therefore, blocked by hydrogen in hydroformylation reaction. High H/Pd ratio (see Table) could be due to H2 spillover. It has been observed that only small adsorption of propylene and CO occurred on catalysts studied. The TPD spectra of CO obtained for bimetallic catalysts consist of two peaks (Fig. 2). The first one was within 15O-19O0C, the second, of low intensity, was found to have desorption rate maximum at 500OC. The last peak could be attributed to CO adsorbed on mixed Pd-Ln"' sites, since only one peak at 15OoCis present in TPD srectrum of monometallic Pd catalyst.
P
1.2
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fl.O
w 0.8 E
z
0
-0.8 x
0.6
W0.6
2!
0
$j0.4 W
g0.4
w
0.2
kO.2 0.0
0.0 TIME, MIN
TIME. MIN
Figure 1. The H2 TPD spectra for 3.2%Pd/Si02 (11, (1.6%Pd+2.9%Ce)/SiO2 (21, and (3.8%Pd+5.O%Pr)/SiOz (3) catalysts. A - pretreatment in hydrogen at 5OoC,B - at 30OoC.
2033
8 1.8
500
F
400
Y
% la2
$ 0.8
300 200
v)
& 0.4
100
0
0.0 TIME, MIN
Figure 2. The CO TPD spectra for 3.2%Pd/SiOz (l), (1.6%Pd+2.9%Ce)/SiOz (21, and (3.8%Pd+S.O%Pr)/SO2 (3) catalysts.
Table Hydroformylation of propylene at 50°C and methanol synthesis at 2SO°C on silica supported Pd+Ln catalysts
Catalysts
1.4%Pd+2.5%La/SiOz 1.6%Pd+2.9%Ce/SiOz 3.8 %Pd+S.O%Pr/SiOz 2.3%Pd+2.7%Sm/SiOz 2.1 %Pd+4.8%Dy/SiOz 2.1 %Pd+7.7%Ho/SiOz 2.5% Pd+4.3%Tm/SiOz 2.1 %Pd+0,6%Yb/SiOz 3.2% Pd/Si02
Activity in propylene hydroformylation' C3Hs
Oxygenatesb
7.4 4.7 4.5 5.5 6.4 4.3
1.6 0.7 0.0 0.6 0.0 0.0
7.9 9.6
1.3 3.0
5.0
0.5
Activity in methanol synthesis'
3.0 7.3 10.0 6.0 6.1 8.2 4.7 2.7 1.o
H/Pdd
soo 3oO0 13.7 1.0 15.2 2.8
12.2 0.4 5.2 0.5
ammol+mmolPd~l+min~' ; bn-C3H7CHO+iso-C3H7CHO; cmmolCO*molPd~l*s~'; dcalculated from TPD data
Some results for the hydroformylation of propylene at 50°C and methanol synthesis are shown in Table. Both the hydroformylation and hydrogenation activities appeared to decrease for the all (Pd+Ln)/SiOz catalysts in comparison to those of Pd/SiOz . The selectivity towards hydroformylation also decreased on the Ln-containing Pd catalysts. Hydrogen pretreatment of the studied catalysts leads to the decrease of hydroformylation activity. 0.5% Pd/La203 catalyst has shown hydrogenation activity only. The similar results for (Pd+Ln) /support catalysts in hydroformylation of hexene- 1 have been obtained. In general, the catalysts of highest hydroformylation activity exhibit lowest activity in methanol synthesis. There seems to be a correlation between H/Pd ratio of catalysts studied and their catalytic properties (see Table). (2.1 %Pd+0.6%Yb)/SiOzand3.2%Pd Kineticsof C3H7CHOand C~H~formationon /SO2 catalysts has been studied. The reaction of propylene hydroformylation has lower hydrogen and propylene reaction order and less negative CO order in comparison to the reaction of propylene hydrogenation. Both hydroformylation and hydrogenation on the two studied catalysts had close kinetics parameters. This suggests that propylene hydroformylation on the catalysts should employ the same mechanism. Single Pd atoms on the support surface could be active sites of hydroformylation reaction. However, some agglomeration would take place following temperature increase. Thus, agglomeration should be responsible for the decrease of hydroformylation activity upon catalysts reduction at elevated temperatures. Fast hydrogenolysis of alkyl - palladium bond (i.e. prior to CO insertion) on Ln-containing Pd catalysts makes them free of hydroformylation activity. 4. CONCLUSIONS
(i) Some of (Pd+Ln) /support catalysts having low frequency mode of adsorbed CO show no activity in olefins hydroformylation. The level of catalytic activity of other catalysts is lower than that of unmodified Pd catalyst where low frequency mode of adsorbed CO is not observed. These reasons allow to suggest that the low frequency mode of adsorbed CO should not insert into metal-alkyl bond on Pd surface. (ii) There seems to be a correlation between hydrogen spillover, CO activation on mixed sites of Ln-modified Pd catalysts and their catalytic activity in methanol synthesis. 5. REFERENCES 1 A.Fukuoka, M.Ichikawa, J.A.Hriljac and D.F.Shriver, Inorg. Chem., 26 (1987) 3543. 2 Yu.A.Ryndin, Yu.N.Nogin, Yu.B.Zverev, N.P.Chernyaev, F.G.Abdikova, and Yu.I.Yermakov, React. Kinet. Catal. Lett.,31 (1986) 151. 3 Yu.N.Nogin, E.A.Paukshtis, A.V.Pashis, and Yu.A.Ryndin, J. Mol. Catal., 55 (1989) 8
Proceedings of the 10th International Congress on Catalysis, 19-24 July, 1992, Budapest, Hungary 0 1993 Elsevier Science Publishers B.V.All rights reserved
THE ROLE OF VARIOUS MODES OF ADSORBED CO IN SYNTHESIS GAS CONVERSION ON LANTFIANIDE IONS PROMOTED BY SUPPORTED Pd CATALYSTS Yu. N. Nogina, N. V. Chesnokovband V. I. Kovalchukb
aInstituteof Catalysis, Russian Academy of Sciences, Siberian Division, 5 Akademika Lavrentieva Str., 630090 Novosibirsk, Russia bInstitute of Chemistry of Natural Organic Materials, 42 K. Marx Str., 660049 Krasnoyarsk, Russia
1. INTRODUCTION
Some dispersed supported metals (for example Pd or Rh) show catalytic activity in vapor phase olefin hydroformylation. The reaction can be used for the study of migratory CO insertion as an elementary step in the alcohols formation and chain propagation in synthesis gas conversion. It is known that the modification of supported rhodium by Fe(II1) ions results in the enhancement of oxygenates formation in propylene hydroformylation. This fact has been accounted by the promotion of migratory CO insertion due to its bi-site activation on surface bimetallic Rh-Fe3+ ensembles [ 11. To understand the role of CO adsorption mode in synthesis gas conversion on modified supported Pd catalysts we have studied propylene and hexene- 1 hydroformylation on supported Pd+Ln and Pd catalysts. 2. EXPERIMENTAL
Silica (surface area, 250 m'g-') and lanthana (60 m'8-I) were used as supports. Tris (isopropylcyclopentadienyl)complexes of Ln and allylpalladiumcyclopentadieny 1 were used as initial compounds. (Pd+Ln)/support catalysts were prepared in an inert atmosphere as described elsewhere [2]. IR spectra were recorded on a Bruker IFS-113 V Fourier spectrometer within 1300-4000 cm-' with a resolution of 4 cm-' as described elsewhere [3]. Temperature programmed desorption (TPD) of hydrogen was carried out following treatment of catalysts by hydrogen at 5OoCand cooling the sample in Hz flow to room temperature. Moreover, the TPD of HZwas carried out following hydrogen processing at 3OO0C and cooling the catalyst in Ar flow to 5OoCand HZadsorption. TPD of CO and propylene was carried out following catalysts reduction by hydrogen at 5OO0C and cooling the sample in helium to room temperature and appropriate gas adsorption.
2032 CO hydrogenation was performed on catalysts reduced at 3OO0C in a copper flow reactor at 25OoC, 10 atm, CO:Hz'l:2, space feed velocity 20 000 h-' with a conversion of <1% as described previously [2]. The activity and selectivity were determined in 30 min upon reaction start. Propylene and hexene- 1 hydrofoimylation was performed on catalysts without any preliminary treatment in a glass flow reactor at 5OoC, 1 atm, C0:Hz:olefin = 1:l:l with a conversion of <5%. Steady state activity and selectivity were determined. 3. RESULTS AND DISCUSSION
FTIR studies of CO adsorption were performed on Ln-containing and unmodified sup orted Pd catalysts. For CO two absorption bands within 2103-2060 and 1975-1900 cm- were reasonably assigned to linear and bridging carbonyl on Pd atoms, respectively. A low-frequency band within 1628-1600 cm-' on modified catalysts can be attributed to CO adsorbed on mixed Pd-Ln"' sites. The reactivity of surface carbonyl species on (1.O%Pd+5.0%Pr)/SiOz catalyst in relation to hydrogen has been investigated.The low-frequency CO adsorption mode does not seem to have the highest reactivity. The results of H2 TPD study for a number of (Pd+Ln) h i 0 2 catalysts are presented on Fig. 1. There are two adsorbed modes of H2 desorbing within 85-12OoC and 365-420°C, with negligible amount of hydrogen being desorbed at low temperature. A considerable part of palladium surface in modified catalysts is, therefore, blocked by hydrogen in hydroformylation reaction. High H/Pd ratio (see Table) could be due to H2 spillover. It has been observed that only small adsorption of propylene and CO occurred on catalysts studied. The TPD spectra of CO obtained for bimetallic catalysts consist of two peaks (Fig. 2). The first one was within 15O-19O0C, the second, of low intensity, was found to have desorption rate maximum at 500OC. The last peak could be attributed to CO adsorbed on mixed Pd-Ln"' sites, since only one peak at 15OoCis present in TPD srectrum of monometallic Pd catalyst.
P
1.2
1 .o
>
fl.O
w 0.8 E
z
0
-0.8 x
0.6
W0.6
2!
0
$j0.4 W
g0.4
w
0.2
kO.2 0.0
0.0 TIME, MIN
TIME. MIN
Figure 1. The H2 TPD spectra for 3.2%Pd/Si02 (11, (1.6%Pd+2.9%Ce)/SiO2 (21, and (3.8%Pd+5.O%Pr)/SiOz (3) catalysts. A - pretreatment in hydrogen at 5OoC,B - at 30OoC.
2033
8 1.8
500
F
400
Y
% la2
$ 0.8
300 200
v)
& 0.4
100
0
0.0 TIME, MIN
Figure 2. The CO TPD spectra for 3.2%Pd/SiOz (l), (1.6%Pd+2.9%Ce)/SiOz (21, and (3.8%Pd+S.O%Pr)/SO2 (3) catalysts.
Table Hydroformylation of propylene at 50°C and methanol synthesis at 2SO°C on silica supported Pd+Ln catalysts
Catalysts
1.4%Pd+2.5%La/SiOz 1.6%Pd+2.9%Ce/SiOz 3.8 %Pd+S.O%Pr/SiOz 2.3%Pd+2.7%Sm/SiOz 2.1 %Pd+4.8%Dy/SiOz 2.1 %Pd+7.7%Ho/SiOz 2.5% Pd+4.3%Tm/SiOz 2.1 %Pd+0,6%Yb/SiOz 3.2% Pd/Si02
Activity in propylene hydroformylation' C3Hs
Oxygenatesb
7.4 4.7 4.5 5.5 6.4 4.3
1.6 0.7 0.0 0.6 0.0 0.0
7.9 9.6
1.3 3.0
5.0
0.5
Activity in methanol synthesis'
3.0 7.3 10.0 6.0 6.1 8.2 4.7 2.7 1.o
H/Pdd
soo 3oO0 13.7 1.0 15.2 2.8
12.2 0.4 5.2 0.5
ammol+mmolPd~l+min~' ; bn-C3H7CHO+iso-C3H7CHO; cmmolCO*molPd~l*s~'; dcalculated from TPD data
Some results for the hydroformylation of propylene at 50°C and methanol synthesis are shown in Table. Both the hydroformylation and hydrogenation activities appeared to decrease for the all (Pd+Ln)/SiOz catalysts in comparison to those of Pd/SiOz . The selectivity towards hydroformylation also decreased on the Ln-containing Pd catalysts. Hydrogen pretreatment of the studied catalysts leads to the decrease of hydroformylation activity. 0.5% Pd/La203 catalyst has shown hydrogenation activity only. The similar results for (Pd+Ln) /support catalysts in hydroformylation of hexene- 1 have been obtained. In general, the catalysts of highest hydroformylation activity exhibit lowest activity in methanol synthesis. There seems to be a correlation between H/Pd ratio of catalysts studied and their catalytic properties (see Table). (2.1 %Pd+0.6%Yb)/SiOzand3.2%Pd Kineticsof C3H7CHOand C~H~formationon /SO2 catalysts has been studied. The reaction of propylene hydroformylation has lower hydrogen and propylene reaction order and less negative CO order in comparison to the reaction of propylene hydrogenation. Both hydroformylation and hydrogenation on the two studied catalysts had close kinetics parameters. This suggests that propylene hydroformylation on the catalysts should employ the same mechanism. Single Pd atoms on the support surface could be active sites of hydroformylation reaction. However, some agglomeration would take place following temperature increase. Thus, agglomeration should be responsible for the decrease of hydroformylation activity upon catalysts reduction at elevated temperatures. Fast hydrogenolysis of alkyl - palladium bond (i.e. prior to CO insertion) on Ln-containing Pd catalysts makes them free of hydroformylation activity. 4. CONCLUSIONS
(i) Some of (Pd+Ln) /support catalysts having low frequency mode of adsorbed CO show no activity in olefins hydroformylation. The level of catalytic activity of other catalysts is lower than that of unmodified Pd catalyst where low frequency mode of adsorbed CO is not observed. These reasons allow to suggest that the low frequency mode of adsorbed CO should not insert into metal-alkyl bond on Pd surface. (ii) There seems to be a correlation between hydrogen spillover, CO activation on mixed sites of Ln-modified Pd catalysts and their catalytic activity in methanol synthesis. 5. REFERENCES 1 A.Fukuoka, M.Ichikawa, J.A.Hriljac and D.F.Shriver, Inorg. Chem., 26 (1987) 3543. 2 Yu.A.Ryndin, Yu.N.Nogin, Yu.B.Zverev, N.P.Chernyaev, F.G.Abdikova, and Yu.I.Yermakov, React. Kinet. Catal. Lett.,31 (1986) 151. 3 Yu.N.Nogin, E.A.Paukshtis, A.V.Pashis, and Yu.A.Ryndin, J. Mol. Catal., 55 (1989) 8